The organization of the developing vertebrate head involves a series of interactions between anterior neural tube, cranial neural crest cells (NCCs), head mesoderm, surface ectoderm and pharyngeal endoderm. Cranial NCCs play an essential role in sculpting the craniofacial structures, such that disruption of cranial neural crest (NC) migration or differentiation results in craniofacial defects -- the most common category of birth defects in humans. Cranial NCCs are generated in the dorsal hindbrain and migrate into the head periphery in three primary streams to populate the corresponding pharyngeal arches with cartilage, pigment, neurons and glia. The mechanisms underlying the patterning of these distinct migratory cranial NC streams have remained elusive. Cranial NC streams fail to separate in a zebrafish mutation encoded by a homeobox transcription factor lazarus (Izr)/pbx4. I propose to study the control and regulation of cranial NC migration by identifying the cause of the lzr/pbx4 cranial NC phenotype at cellular, molecular and genetic levels. In the first specific aim of this proposal, I will attempt to determine the signal that regulates the cranial NC migration by cell labeling and genetic mosaic analyses of wild type and lzr embryos. My preliminary results show that the lzr cranial NC fusion phenotype can be rescued by knocking down the expression of neuropilin 2 (Npn-2), a binding receptor for class 3 secreted semaphorin 3C and 3F and vascular endothelial growth factors in vertebrates. In the second specific aim, I will identify and characterize upstream binding ligands of zebrafish Npn-2 that are essential in the formation of the aberrant cranial NC fusion stream in lzr embryos. In addition, I will perform a suppressor genetic screen to identify mutations that are encoded by genes essential for the lzr dependent cranial NC migration. By dissecting the basic mechanisms involved in controlling cranial NC migration, we should gain insight into how the vertebrate head is patterned and constructed during development. [unreadable] [unreadable]